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SOUND(4)               FreeBSD Kernel Interfaces Manual               SOUND(4)

NAME
     sound, pcm, snd - FreeBSD PCM audio device infrastructure

SYNOPSIS
     To compile this driver into the kernel, place the following line in your
     kernel configuration file:

           device sound

     Non-PnP sound cards require the following lines in device.hints(5):

           hint.pcm.0.at="isa"
           hint.pcm.0.irq="5"
           hint.pcm.0.drq="1"
           hint.pcm.0.flags="0x0"

DESCRIPTION
     Note: There exists some ambiguity in the naming at the moment (sound,
     pcm, snd).  It will be resolved soon by renaming device sound to device
     snd, and doing associated changes.

     The sound driver provides support for PCM audio play and capture.  This
     driver also supports various PCI, ISA, WSS/MSS compatible sound cards,
     AC97 mixer and High Definition Audio.  Once the sound driver attaches,
     supported devices provide audio record and playback channels.  The
     FreeBSD sound system provides dynamic mixing ``VCHAN'' and rate
     conversion ``soft formats''.  True full duplex operation is available on
     most sound cards.

     If the sound card is supported by a bridge driver, the sound driver works
     in conjunction with the bridge driver.

     Apart from the usual parameters, the flags field is used to specify the
     secondary DMA channel (generally used for capture in full duplex cards).
     Flags are set to 0 for cards not using a secondary DMA channel, or to
     0x10 + C to specify channel C.

     The driver does its best to recognize the installed hardware and drive it
     correctly so the user is not required to add several lines in
     /boot/device.hints.  For PCI and ISA PnP cards this is actually easy
     since they identify themselves.  For legacy ISA cards, the driver looks
     for MSS cards at addresses 0x530 and 0x604 (unless overridden in
     /boot/device.hints).

   Boot Variables
     In general, the module snd_foo corresponds to device snd_foo and can be
     loaded by the boot loader(8) via loader.conf(5) or from the command line
     using the kldload(8) utility.  Options which can be specified in
     /boot/loader.conf include:

           snd_driver_load       (``NO'') If set to ``YES'', this option loads
                                 all available drivers.

           snd_emu10k1_load      (``NO'') If set to ``YES'', only the
                                 SoundBlaster 5.1 driver and dependent modules
                                 will be loaded.

           snd_foo_load          (``NO'') If set to ``YES'', load driver for
                                 card/chipset foo.

     To define default values for the different mixer channels, set the
     channel to the preferred value using hints, e.g.: hint.pcm.0.line="0".
     This will mute the input channel per default.

   VCHANs
     Each device can optionally support more playback channels than physical
     hardware provides by using ``virtual channels'' or VCHANs.  VCHAN options
     can be configured via the sysctl(8) interface but can only be manipulated
     while the device is inactive.

   Runtime Configuration
     The following sysctl(8) variables are available:

           hw.snd.pcm%d.buffersize         Configure the amount of DMA
                                           bufferspace available for a device.

           hw.snd.targetirqrate            Set the default block size such
                                           that continuous playback will
                                           achieve this IRQ rate.  This value
                                           can be tuned to improve application
                                           performance.  Increase this value
                                           when the sound lags and decrease it
                                           if sound stutters or breaks up.

           hw.snd.unit                     When using devfs(5), the default
                                           device for /dev/dsp.  Equivalent to
                                           a symlink from /dev/dsp to
                                           /dev/dsp${hw.snd.unit}.

           hw.snd.report_soft_formats      Controls the internal format
                                           conversion if it is available
                                           transparently to the application
                                           software.  When disabled or not
                                           available, the application will
                                           only be able to select formats the
                                           device natively supports.

           hw.snd.verbose                  Level of verbosity for the
                                           /dev/sndstat device.  Higher values
                                           include more output and the highest
                                           level, three, should be used when
                                           reporting problems.  Other options
                                           include:

                                           0   Installed devices and their
                                               allocated bus resources.

                                           1   The number of playback, record,
                                               virtual channels, and flags per
                                               device.

                                           2   Channel information per device
                                               including the channel's current
                                               format, speed, and pseudo
                                               device statistics such as
                                               buffer overruns and buffer
                                               underruns.

                                           3   File names and versions of the
                                               currently loaded sound modules.

           hw.snd.maxautovchans            Global VCHAN setting that only
                                           affects devices with only one
                                           playback channel available.  The
                                           sound system will dynamically
                                           create up this many VCHANs.  Set to
                                           ``0'' if no VCHANS are desired.

           hw.snd.pcm%d.vchans             The current number of VCHANs
                                           allocated per device.  This can be
                                           set to preallocate a certain number
                                           of VCHANs.  Setting this value to
                                           ``0'' will disable VCHANs for this
                                           device.

   Recording Channels
     On devices that have more than one recording source (ie: mic and line),
     there is a corresponding /dev/dspr%d.%d device.

   Statistics
     Channel statistics are only kept while the device is open.  So with
     situations involving overruns and underruns, consider the output while
     the errant application is open and running.

   IOCTL Support
     The driver supports most of the OSS ioctl() functions, and most
     applications work unmodified.  A few differences exist, while memory
     mapped playback is supported natively and in Linux emulation, memory
     mapped recording is not due to VM system design.  As a consequence, some
     applications may need to be recompiled with a slightly modified audio
     module.  See <sys/soundcard.h> for a complete list of the supported
     ioctl() functions.

FILES
     The sound drivers may create the following device nodes:

     /dev/audio%d.%d      Sparc-compatible audio device.
     /dev/dsp%d.%d        Digitized voice device.
     /dev/dspW%d.%d       Like /dev/dsp, but 16 bits per sample.
     /dev/dspr%d.%d       Should be connected to a record codec.
     /dev/sndstat         Current sound status, including all channels and
                          drivers.

     The first number in the device node represents the unit number of the
     sound device.  All sound devices are listed in /dev/sndstat.  Additional
     messages are sometimes recorded when the device is probed and attached,
     these messages can be viewed with the dmesg(8) utility.

DIAGNOSTICS
     ac97: dac not ready  AC97 codec is not likely to be accompanied with the
     sound card.

     unsupported subdevice XX  A device node is not created properly.

SEE ALSO
     snd_ad1816(4), snd_als4000(4), snd_atiixp(4), snd_audiocs(4), snd_cmi(4),
     snd_cs4281(4), snd_csa(4), snd_ds1(4), snd_emu10k1(4), snd_envy24(4),
     snd_envy24ht(4), snd_es137x(4), snd_ess(4), snd_fm801(4), snd_gusc(4),
     snd_hda(4), snd_ich(4), snd_maestro(4), snd_maestro3(4), snd_mss(4),
     snd_neomagic(4), snd_sbc(4), snd_solo(4), snd_spicds(4), snd_t4dwave(4),
     snd_uaudio(4), snd_via8233(4), snd_via82c686(4), snd_vibes(4), devfs(5),
     device.hints(5), loader.conf(5), dmesg(8), kldload(8), sysctl(8)

     The OSS API, http://www.opensound.com/pguide/oss.pdf.

HISTORY
     The sound device driver first appeared in FreeBSD 2.2.6 as pcm, written
     by Luigi Rizzo.  It was later rewritten in FreeBSD 4.0 by Cameron Grant.
     The API evolved from the VOXWARE standard which later became OSS
     standard.

AUTHORS
     Luigi Rizzo <luigi@iet.unipi.it> initially wrote the pcm device driver
     and this manual page.  Cameron Grant <gandalf@vilnya.demon.co.uk> later
     revised the device driver for FreeBSD 4.0.  Seigo Tanimura
     <tanimura@r.dl.itc.u-tokyo.ac.jp> revised this manual page.  It was then
     rewritten for FreeBSD 5.2.

BUGS
     Some features of your sound card (e.g., global volume control) might not
     be supported on all devices.

FreeBSD 11.0-PRERELEASE        November 26, 2006       FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | FILES | DIAGNOSTICS | SEE ALSO | HISTORY | AUTHORS | BUGS

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